Prostate cancer is an age-dependent disease. There is currently no treatment that can prevent the development and/or progression of this deadly disease. Most of the work to date has focused on the advanced stages of prostate cancer. Very little work has been directed toward the prevention of prostate cancer during the early stages of this disease. A large number of epidemiological studies have suggested that phytoestrogens in soybean can reduce the risk for acquisition of hormone-dependent cancers. Several studies have demonstrated that genistein, the most abundant isoflavone present in soy, is responsible for this beneficial outcome. TRAMP (Transgenic Adenocarcinoma of Mouse Prostate) mice develop age-dependent progressive forms of prostatic disease that histologically resemble human prostate cancer. Therefore, using the TRAMP model, we propose to investigate the effects of genistein on age-dependent and stage-specific development of prostatic carcinoma and establish the molecular mechanism(s) of growth inhibition. The specific aims of this proposal are: First, we will determine the effects of genistein on the age-dependent development and progression of prostate cancer in TRAMP mice. To do so, TRAMP mice, before developing tumors, and mice bearing different stages of prostate cancer, will be treated with genistein for different time periods. Prostatic histopathology, cell proliferation and cell death will be examined in untreated vs. genistein-treated groups. Second, we will examine possible mechanisms by which genistein inhibits cell proliferation of prostate cancer in TRAMP mice in vivo, and in TRAMP cell lines (C1 and C2) in vitro. Specifically, we will investigate the effects of genistein on growth factor (TGF-alpha and/or IGF-I)-induced expression of cell cycle regulatory proteins and MAPK and PI3K pathways in TRAMP cell lines and in TRAMP dorsolateral prostate. Third., to examine the mechanisms of genistein-induced cell death, alterations in cell survival factors, pro-apoptotic and anti-apoptotic proteins and activation of caspase pathways will be evaluated in TRAMP dorsolateral prostate and/or TRAMP cell lines. This project will demonstrate the efficacy of genistein in early prevention of prostate cancer, and the mechanism of action underlying the prostate cancer suppressing activity of genistein. This information will lead to more effective prostate cancer prevention and control strategies in humans.